This invention relates to a method of producing shaped glass articles including glass composited articles by chemical vapor desposition. The invention is especially concerned with a method of preparing silica-type glass bodies of exceptionally high purity under controlled conditions.
Typical processes for preparing high silica glasses include fusion of quartz and acid leaching of phase separated borosilicate glasses. The resultant high silica containing material generally is heated at elevated temperatures and consolidated prior to shaping.
It is also known to form shaped silica articles by flame hydrolysis. Briefly, in this technique a stream of gas entraining a compound of silicon is introduced into the flame of a combustible gas. The compound of silicon is hydrolyzed to form amorphous silica which is desposited on a mandrel.
Preparation of glass by the fusion and acid leaching techniques outlined above is often costly and does not lend itself well to forming composite glass articles, particularly those in which a silica is deposited on the surface of a substrate in a very thin adherent layer. The flame hydrolysis technique lends itself to deposition of silica on a mandrel. However, the number of suitable volatile silica compounds that can be used by the flame hydrolysis technique is quite limited and, more importantly, deposition of uniform controlled amounts of fused silica-type glass by this technique is quite difficult, expecially on very thin, small and delicate mandrels of intricate shapes.